90 Dodge Truck 2500

My son just bought this 90 dodge 2500 cummins truck from a guy we work with. said it did not run trouble with the head or fuel pump and if anybody knows the fuel pump on this thing is very prices.. oh he bought it for 1500 dollars . got it home put a battery in it hit the starter it fired right up no black or white smoke at all . it runs like a top . we went to work the next day an told steve the that truck he sold my son run just fine . corey drove it around the block and to the store just to see how it run he came back home an said it did fine. that kid of mine is so lucky.. what is was was a red wire had came off the battery that ran everything . so corey put the wire back on the battery an it fried up after setting for over a year.. long story short.